THE FRONT OF THE THIGH 411 



membrane and the medial margin of the foramen, and its tendon passes 

 laterally, to be inserted into the trochanteric fossa. It lies deeply in the 

 interval between the quadratus femoris and the inferior gemellus, and is at 

 first below and then posterior to the capsule of the hip-joint. It is supplied 

 by the posterior branch of the obturator nerve (I,. 3 and 4), and acts as a 

 powerful lateral rotator of the thigh. 



Owing to the tilt of the pelvis, the outer surface of the muscle is directed 

 distally, laterally, and forwards. It is in relation to the pectineus and the 

 adductor brevis. 



The Obturator Nerve (L. 2, 3, 4) breaks up into an 

 anterior and a posterior division as it enters the upper part 

 of the obturator foramen. The anterior division leaves the pelvis 

 above the obturator externus, and passes distally, first between 

 that muscle and the pectineus, and then between the adductors 

 brevis and longus. It supplies the two last-named muscles 

 and the gracilis, and in addition gives an articular branch to 

 the hip- joint. Further, it gives origin to a small branch 

 which unites with a similar branch from the medial cutaneous 

 to form the sartorial plexus. Twigs from this plexus, which 

 lies deep to the sartorius, supply the skin on the medial side 

 of the thigh. 



The posterior division pierces the upper part of the obturator 

 externus, which it supplies, and descends on the deep surface 

 of the adductor brevis. It supplies the adductor magnus and 

 gives off a fine articular branch to the knee-joint (p. 406). 



The Obturator Artery (p. 405) accompanies the anterior 

 division of the obturator nerve through the foramen. It 

 divides into two branches, which encircle the obturator mem- 

 brane deep to the obturator externus, supplying the muscle 

 and giving off a branch to the hip- joint (p. 438). 



Obturator Hernia is of rare occurrence. It follows the 

 vessels and nerve through the upper part of the obturator 

 foramen but has no constant relation to them. The protrusion, 

 however, causes pressure on the nerve and gives rise to Romberg's 

 symptom. This consists in tenderness of the adductors, and 

 pain referred to the cutaneous distribution of the obturator 

 nerve on the medial side of the thigh. 



The hernia, which is usually strangulated, lies behind the 

 pectineus and on the surface of the obturator externus, causing 

 a small, ill-defined swelling in the medio-proximal part of the 

 thigh ; the thigh is kept flexed in order to relax the pectineus, 

 and attempts to produce extension cause severe pain. Adduc- 

 tion is also resisted, as this movement tends to squeeze the 

 hernia against the obturator externus. 



